Andy, I have been studying the chassis loom diagrams both pre and post 2014 in an attempt to discover purpose of extra relay. Both diagrams show five relays with the early diagram showing fifth as flasher relay and later one as cooling fan. I'm guessing the flasher relay was incorporated in TSM unit for later models as this has 18 pin connector (two pins unused) against 12 pin one on earlier versions.
This doesn't help with identifying extra relay though so looked closely at cable colours to it. A red/blue (RU) cable can be seen which is unique in providing power to rear fog lamp. Thoughts are that relay may be to inhibit rear fog when headlights not on therefore although not shown on diagrams. Pure speculation of course.
The black box you queried is described as dip/main beam unit although unsure of its need as you already have two standalone relays to handle dip/main and headlamp flash
